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Compiler-specific Features
Usage
__align(n) is useful when the normal alignment of the variable being declared is less
than n. Eight-byte alignment can give a significant performance advantage with VFP
instructions.
__align can be used in conjunction with extern and static.
Restrictions
Because __align is a storage class modifier, it cannot be used on:
• types, including typedefs and structure definitions
• function parameters.
You can only overalign. That is, you can make a two-byte object four-byte aligned but
you cannot align a four-byte object at 2 bytes.
Examples
__align(8) char buffer[128]; // buffer starts on eight-byte boundary
void foo(void)
{
...
__align(16) int i; // this alignment value is not permitted for
// a local variable
...
}
__align(16) int i; // permitted as a global variable.
See also
• --min_array_alignment=opt on page 2-91 in the Compiler User Guide.
4.1.2 __alignof__
The __alignof__ keyword enables you to enquire about the alignment of a type or
variable.
Note
This keyword is a GNU compiler extension that is supported by the ARM compiler.
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